Agriculture is a major industry in the U.S., which is a net exporter of food. As of 2010 there were approximately 2.2 million farms in the U.S. covering an area of approximately 920 million acres. In 1800 approximately ninety percent of the entire U.S. population was employed in agriculture, and present day numbers have dropped to approximately two percent due largely to the development and implementation of large, automated agricultural equipment, such as combine harvesters, which have replaced large numbers of farm workers.
The crops grown in the U.S., such as wheat, barley, and rye, are only partly edible. While the seeds or grains at the top of each plant are edible and useful for making products such as bread and cereal, the rest of the plant, which is the chaff, is inedible and has to be discarded. Before modern-day machines were developed, such as in the 1800's, agricultural workers had to harvest crops by carrying out a series of laborious operations one after another. First they had to cut down the plants with a long-handled cutting tool such as a scythe. Next, they had to separate the edible grain from the inedible chaff by beating the cut stalks in an operation known as threshing. Finally, they had to clean any remaining debris away from the seeds to make them suitable for use in a mill. All this took a considerable amount of time and labor requiring large numbers of farm workers. The modern combine harvester carries out these various operations automatically eliminating the need for numerous farm workers.
Agricultural combines harvest an agricultural crop, thresh the harvested crop to break the large crop components from the smaller crop components, separate the smaller crop components from the larger crop components, and clean the smaller components to eliminate chaff from the grain. In operation, a combine harvester is driven through a field of a growing crop, whereby the combine harvester harvests, threshes, and winnows or separates the grain from the chaff. The grain collects in a tank inside the combine harvester, which is periodically emptied into tractors that drive alongside, and the chaff is ejected onto the field from an ejection spout at the back of the combine harvester. The combine may be equipped with various harvesting assemblies including grain platforms (rigid and flexible), corn headers, row crop headers or windrow pickup platforms depending on the crop and the harvesting practices employed by the farmer. The threshing assembly of the combine may be configured in a number of different ways, including a conventional transverse threshing cylinder and concave, or a rotary threshing system that is either axially of transversely arranged. In addition, the separating assembly may comprise conventional straw walkers or rotary assemblies.
In general, a combine harvester includes a header, a pickup reel, a cutter, a threshing assembly including a threshing drum and concave, a separating assembly, a cleaning assembly, a collection tank, and conveyors, such as rotating belts and spinning augers. The header gathers the crop, and the pickup reel pushes the crop down toward the cutter, which cuts the crop at the base near ground level. A conveyor picks up the cuttings from the cutter, and conveys the cuttings to the threshing drum, which rotates and threshes the cuttings against the concave separating the grains from the chaff to form threshings, namely, the chaff and the separated grains. The threshings are then applied to the cleaning assembly from the separating assembly.
The cleaning assembly removes chaff from the grain. The cleaning assembly typically includes a cleaning shoe and a cleaning fan. The smaller crop components from the threshing assembly and the separating assembly are directed to the cleaning shoe. The cleaning shoe typically is provided with a chaffer and a sieve. The chaffer and sieve have transverse louvers that define openings. The heavier clean grain falls through the openings formed by the louvers on the chaffer and the sieve. The air blast from the cleaning fan blows the chaff out the rear of the combine.
There are three types of cleaning shoe actions, namely, reciprocating, shaker and cascading. In a reciprocating shoe the chaffer and sieve move in opposite directions to one another. In a shaker shoe the chaffer and sieve move in the same direction at the same time. In a cascading shoe the chaffers and sieve are positioned so that the small components drop from one unit to another in a cascading or rolling motion.
The operational efficiency of a combine harvester is proportional to variations in loading across the threshing, separating, and cleaning assemblies caused principally by variations in crop feedrate caused by variations in combine ground speed and crop condition. In about the 1980s, on-board electronics were introduced to measure threshing efficiency. This new instrumentation allowed operators to get better grain yields by optimizing ground speed and other parameters via the operator controls in the cab of the combine. This required the farmer to constantly monitor the threshing efficiency measurements and make period adjustments to ground speed and other parameters, which proved cumbersome and tiresome and largely impracticable. Recent developments have attempted to solve this problem with ground speed controls that automatically adjust combine ground speed in response to through-put measurements. Although the implementation of such speed control units has been shown to improve grain yield, speed adjustments increase fuel consumption and strain engine components and drive trains.